Pressor responses to hyperventilation in normotensive and hypertensive elderly subjects.

Background: Recently we showed that the hyperventilation test induces different blood pressure (BP) responses both in healthy subjects and patients with essential hypertension. Aim: We evaluated whether pressor responses to hyperventilation change with aging in normotensive and hypertensive subjects and whether they are related to the daytime pressor profile. Methods: Forty-three elderly normotensive subjects and 94 elderly hypertensive patients (45 with essential hypertension and 49 with secondary hypertension) underwent five minutes of forced hyperventilation and daily ambulatory BP monitoring. Results: Hyperventilation did not significantly change BP in normotensive subjects and secondary hypertensive patients, whereas it decreased (p<0.01) BP in essential hypertensive patients. Hierarchical cluster analysis based on BP responses to hyperventilation disclosed three groups of subjects in each studied population: group 1 exhibited a reduction (p<0.05) in BP (prevalent in essential hypertensives, 76 %), group 2 no change (prevalent in normotensives, 70 %, and in secondary hypertensives, 76 %), and group 3 an increase (p<0.05). Pressor daytime profiles of hypertensive patients showed significant differences according to pressor responses to hyperventilation. In group 1 patients the peak ambulatory SBP correlated (p<0.01) to the pre-hyperventilation SBP, whereas in group 3 it correlated (p<0.01) to the hyperventilation peak SBP. Group 2 did not show major daily BP fluctuations. Conclusions: 1) Aging decreases reactivity to the effects of respiratory alkalosis in elderly normotensive subjects; 2) hyperventilation induces significant pressor changes overall in essential hypertension; 3) the significant pressor responses to hyperventilation reflect the daytime pressor profiles predicting the highest daily fluctuations of BP values.